The present invention relates generally to an aerosol dispensing device, and in particular, to an aerosol dispensing device having an improved dosage indicator for indicating the number of metered dosages that have been dispensed from, or remain in, the dispensing device.
Aerosol dispensing devices have been developed that include a counting or dose indicating device to indicate the number of metered doses that have been dispensed from the device, or to indicate the number of doses remaining therein. For example, patients have certain conditions that can be treated with medicaments dispersed in an aerosol and administered to the patient by inhalation. In one format, the aerosol and medicaments are contained in a canister, or container, and dispensed in metered, or measured, dosages with an inhalation device, or actuator boot. In such an arrangement, it is important for the patient to be able to ascertain the number of metered doses remaining in the canister, either by an indication of the number remaining therein or by knowledge of the number already dispensed therefrom, such that the patient is not caught unaware with an empty canister when in need of the medicament. Thus, it may be important for the inhalation device to provide an accurate indication of either the number of doses remaining in the canister, or the number of doses already dispensed therefrom.
Typically, a conventional aerosol canister includes a body and a valve stem which can be depressed relative to the body so as to emit the metered dose of aerosol and medicament. The canister is usually supplied with a predetermined number of metered doses, generally on the order of about 200, such that the counting of the number of valve stem depressions, and corresponding number of dispensed metered doses, can be directly correlated with the number of doses remaining in the canister.
In operation, the canister is typically received within a housing of the inhalation device, wherein the valve is brought into engagement with a support block in the housing. The user administers the medicament by moving the canister relative to the housing so as to depress the valve stem and internal valve and thereby release a metered dose, which is typically administered to the user through a port or mouthpiece extending from the housing. After the dose is administered, the valve stem, which is typically spring loaded, biases the canister away from the support block so as to again move the canister relative to the housing. In this way, a metered dose of medicament is administered by each cycle of linear reciprocal movement of the canister relative to the housing.
Some actuator boots have indicating devices that convert the linear reciprocal movement of the canister relative to the housing into a one-way, or single-cycle, movement of an indicator, wherein the indicator identifies the relative fullness of the canister, the number of metered doses remaining therein or the number of doses already administered. Although these actuator boots with indicators have provided the advantage of generally being able to keep track of the number of dosages, there remains room for improvement. For example, indicating devices of this nature may include complex moving parts which can be difficult to assemble and expensive to manufacture. Such devices may also be susceptible to counting inaccuracies due to the configuration of the indexing or mating parts, or require excessive amounts of space within the housing to accommodate the relatively large or numerous moving parts. Others still may impede or interfere with the airflow and medicament being dispensed from the inhalation device. Alternatively, some devices use electrical circuitry to count or record the dispersements. Such devices can be relatively expensive to manufacture, however, and require electrical power and may be more susceptible to damage in various environments, such as moist conditions.